flyback converter

[JAIZY]

I am making a flyback converter for some study purpose but the problem is that i use a step up transformer with ratio of 1:10 and the input is 12 volt dc but the output is only 3 volts can anyone know why this low voltage is at the output.I am attaching a picture also.reply me please what's the logic that the output is less than the input but i am using a step up transformer.
https://www.google.com.pk/imgres?im...wwfT6mKF7CiiAeH3JH0DQ&ved=0CCkQ9QEwAA&dur=255

 

[ronsimpson]

There are some nice ICs that would replace the 555 and BF487 and some even the MOSFET all in one package. This will include current limit.

Do you have a oscilloscope? Can you see the duty cycle on the gate of the MOSFET? If you only have a meter you could measure the DC voltage on the gate. If the supply is 12V and you measure 6V then you have 50% duty cycle. My guess is you will measure about 1 volt. If I could see the waveform on the MOSFET-D I would know more.

Things to check. Phase of transformer. Primary and secondary may be reversed. What transformer are you using?
Is anything getting hot?

 

[Diver300]

I would stick to a boost converter.

https://www.kosbo.com/kitdocs/in17_4d_cl/in17clock_circuit.pdf is an example.

I really can't see that there are big advantages in using a flyback converter unless you need really big voltage ratios or isolation.

 

[simonbramble]

.. is the curren flowing through your resistive divider network on the output enough to turn on that feedback transistor with a very low Vb-e? I cant imagine why it would be so low, but personally I would not rely on the VBE = 0.6V to do any form of regulation. I have written some guides on the principals of flyback converter design and you can simulate them in LTSPICE:
http://www.simonbramble.co.uk/lt_spice/ltspice_lt_spice.htm
Have a look through my site and it will explain the theory of what you are trying to do